Rotatable current lead-in units for furnace crucible



May 5, 1959 o. WINKLER 2,885,647

ROTATABLE CURRENT LEAD-IN UNITS FOR FURNACE CRUCIBLE Filed oct. 24, 1955 IN Vgn/TOR O T70 h//Mg/EQ United States Patent O ROTATABLE CURRENT LEAD-IN UNITS FOR FURNACE CRUCIBLE Otto Winkler, Balzers, Liechtenstein, assignor to Geraetebau-Anstalt, Ballers, Liechtenstein Application ctoher 24, 1955, Serial No. 542,277V Claims priority, application Switzerland October 22, 1954 8 Claims. (Cl. 339-5) This invention relates to means :for conducting electric currents into enclosures, and in particular to rotatable current lead-in devices.

It is an important object of the present invention to provide means facilitating, in simple and highly eiiicient manner, delivery of high-intensity, high-frequency electric current to a movable instrumentality designed for making use of said current, and in particular where such instrumentality is disposed in a substantially inaccessible enclosure.

lt is another object of the present invention to provide means affording a greatly simplified and highly efficacious rotatable current lead-in device for use in connection with closed chambers in which is located shiftable apparatus to which said current is to be delivered from an exterior source via stationary conductors, said device to this end being provided with a rotatable section extending through a wall of said chamber and with a stationary section located exteriorly of said chamber, intermediate conductors leading from said stationary conductors to said apparatus being incorporated in said sections.

Another object of the present invention is the provision of means enabling cooling of high-power conductors constituting portions of a rotatable current lead-in device of the aforesaid type in a manner substantially avoiding the use of auxiliary jackets or tubes for conducting a cooling medium and permitting said medium to ow directly through said device.

Still another object of the present invention is the provision of means contributing to compact and sturdy current lead-in devices in which a hollow rotatable member having torsionable conductors incorporated therein is disposed between a relatively stationary current source and relatively movable means in which said current is used, the arrangement being such that a minimum of torque is necessary to rotate said member, while the current-carrying capacity of said device is maintained at a maximum.

t is still another object of the present invention to provide means contributing to a rotatable current leadin device or unit as described above in which a plurality of torsionable, electrically conductive cables constituting at least the relatively high-potential current flow path are ensheathed in a torsionable, flexible tube and pretorsioned in a direction opposite to the normal direction of rotation of said unit, the angle of said pretorsion being equal to about one half of the total angle through which said unit is normally rotated, whereby the external mechanical power required for rotation of said unit is substantially reduced due to the tendency of said cables to return to an untorsioned state.

A further object of the present invention is to provide means conductive to feeding high-intensity, high-frequency electric current to apparatus located within a substantially sealed enclosure in such a manner as to minimize both the power losses in as well as the cooling requirements for the conductors of said current.

Yet a further object oi the present invention is to provide means redounding to novel and greatly improved current lead-in devices of the aforesaid type which may be inexpensively manufactured, easily installed in all existing facilities, and are completely safe in operation.

More particularly, rotatable current lead-in units or devices iind extensive use in a variety of industrial applications, such as conducting current of high intensity into closed chambers or spaces employed in electric furnaces, smelting plants, foundries and the like. In many of these applications it is necessary to rotate the current conductor in situ since it may be necessary, as in the case of smelting and foundry plants, that molten material disposed 'in one container, e.g. a Crucible, be poured to another, e.g. a mold, within said chamber either under vacuum or under a protective, inert gas atmosphere.

ln accordance with the invention, electrically conductive cables and the necessary cooling arrangement therefor are so disposed in a rotatable shaft that it is possible to conduct into the enclosure currents of much higher intensities than has heretofore been possible with known arrangements.

These and other objects of the invention will become further apparent from the following detailed description, reference being made to the accompanying drawing showing a preferred embodiment of the invention.

In the drawing:

Fig. l is a longitudinal, side elevational view, partly in section, of a representative embodiment of a current lead-in unit constructed in accordance with the present invention;

Fig. 2 is a sectional view taken along in Fig. l; and

Fig. 3 is a partial sectional view in reduced scale of an induction furnace and associated heating coils utilized in coniunction with the invention.

While there is shown and described herein certain specic structure embodying the invention, it will be manifest to those skilled in the art that various modications and rearrangements of the parts may be made without departing from the scope of the invention, and that the same is not limited to the particular form herein shown and described, except in so far as indicated by the appended claims.

Referring now more particularly to the drawing, a bearing housing 2 is disposed in the wall 1 of a closed or sealed vessel, for example the crucible of a vacuum induction furnace, through which wall the heating current is to be conducted to the crucible while at the same time tilting movements are imparted to said Crucible for pouring out therefrom its contents.

The housing 2 presents a suitable bearing, which may be a slide bearing or a ball bearing (not explicity shown in Fig. l), for example. ln the bearing a hollow shaft 3 of a suitable light-weight material, such as aluminum, is rotatably mounted. The shaft 3 is sealingly surrounded by means of a sealing ring 4.

The shaft 3 may be rotated through a predetermined angle by means of suitable driving means (not shown) operatively connected to driven means connected to the shaft, the driven means being represented schematically in Fig. l by a gear 5 fixed to the outer surface of the shaft. ln this manner, an induction heating coil 62 and associated crucible 56 LC., which are attached to the right hand end (in Fig. l) of the shaft, may be tilted or otherwise appropriately moved through rotation of the shaft.

The actual current conducting arrangement includes a torsionabte tube 6 made of elastic insulating material, such as rubber, `wh-ich is located in the interior of shaft 3. One current path, for example, the path which is at an elevated potential with respect to ground, consists of flexible, torsionable cables or conducting elements 7 the line A-A 3 which are disposed at spaced locations along the inner surface of the insulating tube 6 and which, when the heating current is a high-frequency current, are constructed after the fashion of conventional high-frequency cables.

The second current path likewise consists of a number of exible cables or conducting elements 3 which are spaced from each other and which are separated from -the cables 7 by means of tube 6. The cables 8 thus vsurround the tube 6. The individual conducting elements constituting each of the current paths lie liush .against the substantially cylindrical surfaces of the tube 6.

YIn order to ensure that the conducting cables '7 disposed internally of the exible tube 6 lie closely against the inner wall or surface of the latter, a helical spring 43 made of bronze, for example, is provided which tends -to press said cables 7 against said inner surface. Coils 44, 45 and 46, made of wire, for example, surround respective portions of the cables 8 and retain the latter Yagainst the outer surface of the tube 6.

Thus, the two sets of cables are coaxially arranged,

land as a result the inductance of the conducting system as a whole is very small. This is very desirable for the purpose of avoiding induction-caused voltage drops along the coaxial conducting system and for reducing wattless currents. Moreover, should the conducting system not be free of inductance, stray magnetic elds would be created by the very large currents involved, which would result in eddy current losses in the metallic parts -of the rotating lead-in unit.

To absorb and remove the heat generated by the current passing through the conducting cables 7 and S, an

inlet nipple 9 is provided at the outer end of a stationary part of the unit, more fully described below. Through this nipple 9 a cooling medium, such as water,

'may be introduced, as indicated by the arrow 72. Said cooling medium flows relatively rapidly through the center of the tube 6 as indicated by arrows 74 and therefrom through an opening 10 as indicated by arrow 76 in a member 12 having a bore 11 from which the medium streams into the pipe or tubular element 13 as indicated the cooling medium passes, after its temperature has been negligibly increased into a pipe element 15 which has a flange 16 to which flange 60 of the induction furnace 56 is connected. The medium then llows through bores 17 of an intermediate member 18 and into the annular space between the outer surface of the tube 6 and the inner surface of the hollow shaft 3. The cooling medium leaves said space at 19 and is conducted away through an outlet opening or nipple 20. The cooling medium will not be affected by the induction heating eiect which acts primarily on the crucible, `whereby the induction coil is not exposed to considerable heat.

Current is led to and from the lead-in or conductor unit over stationary, water cooled bus bars 21 and 22 of relatively large cross-section for enhancing the electrical conductivity thereof, bus bar 21 being connected to the exible cables 7 located internally of the tube 6 by means of a metallic, externally conically shaped member 23. The cables 7 may be either welded or soldered at one end to the member 23. Bus bar 22 is electrically connected to the metallic, internally conically shaped member 24 which, in turn, is either Welded or soldered to the cables 8 at one end of the latter.

The members 23 and 24 are electrically insulated from each other by means of one extended end of the tube 6 which is located between the conical surfaces of said members, the latter being pressed against one another by means of electrically insulating bolts 25. The remaining ends of the cables 7 are electrically connected to the member 12, while the cables 8 are electrically connected to the intermediate member 1S. The tube 6 is also extended at this end and :litted over the member 12 to such an extent that it insulates the latter from the substantiallyplate-like member 18.

The outer surface of the member 12 is threaded and the pipe element 13, which is internally threaded at one end, is screwed onto said member 12. The current path from the cables 7 thus continues through the pipe 12 and the member 13 to the heating coil 62, one terminal of which is attached to the flange 14. The intermediate member 18 is retained in position between a flange 27 of the hollow shaft 3 and a flange 28 of a pipe element 29 by means of suitable bolts (not shown).

Welded to the pipe element 29 and extending substantially at right angles thereto is the above-mentioned pipe element 15 which serves as the second connecting terminal for the heating coil. Inasmuch as al1 the metallic elements of the conductor unit are preferably made of materials such as aluminum and copper, having good electrical conductivity characteristics, a current path of minimum resistance is established from the cables 8 via the intermediate member 18 and the pipe elements 29 and 15 to the second terminal of the induction heating coil.

The member 12 and pipe 13 are electrically insulated from the elements 29 and 15 by means of a tubular insulating member 26. The conical end portion of the member 12 is drawn toward and lixedly retained against the intermediate member 18 by means of the threaded interengagement between the member 12 and pipe 13, the intermediate member 18 being correspondingly formed with a conical bore. In this manner, the extension of the tube 6 insulates the members 18 and 12 from each other.

Interposed between the adjacent anges of the various portions of the conductor unit are sealing elements 34, 35, 36, 37, 38 and 39, the purpose and function of which Will be more fully explained hereinbelow.

When it is desired to rotate the lead-in unit so as to tilt the heating coil and the crucible associated therewith, the gear 5 is rotated by suitable drive means (not shown). In this manner, all of the structural elements connected to the hollow shaft 3 which are shown on the right hand side of Fig. 1 are rotated. This includes the members 18, 12 and 13, the ends of the cables 7 and 8 attached to said members 12 and 18, and the elements 29 and 15, as well as the apparatus, i.e., the coil and crucible, attached to the flanges 14 and 16.

The parts of the conductor unit shown to the left of the rotating hollow shaft 3 and gear 5 in Fig. l, i.e., the members 23 and 24 and, consequently, the adjacent cable ends and the bus bars 21 and 22 aixed to said members, remain stationary. As a result, the bundles or sets of cables 7 and 8 and the tube 6, as well as each of the individual cables, will be torsioned as the shaft 3 rotates.

The longitudinal dimensions of the cables are so chosen that, prior to initiation of the rotary movement of the shaft, they do not lie exactly along the generatrices of the tube 6 but contact the latter along helical lines of small curvature. The cables are thus pretorsioned in a direction opposite to the ultimate direction of rotation of the shaft 3.

The magnitude of the pretorsion is so chosen that upon rotation of the shaft 3 from its initial end position to its final end position, the first half of the rotation takes place in opposition to the turning of the helix and with the aid of the cables which tend to return to their rectilinear state. Upon further rotation of the shaft, Le., during the second half of said rotation, the cables there will be torsioned into a slight helix turned in a direction opposite to the direction of the above-mentioned helical lines.

In this manner, it becomes possible to employ cables, e.g. high-frequency cables, of relatively larger diameter than when the torsional load is applied in only one direction from a zero position in which said cables are untorsioned. Due to the positions of the cables within the hollow shaft 3, quite apart from the slight helical arrangement thereof, it is possible to employ individual cables of greater width and lesser flexibility than is required when the cables attached to the outer end of one of the known rotating conductor units are flexibly suspended between said unit and the bus bars which are normally approximately 50 cm. away.

The last mentioned difficulty, inherent in known ar rangements of this kind, is complicated even more by the fact that each individual cable requires its own cooling jacket when the current intensity becomes fairly high. In the lead-in or conductor unit according to the present invention, however, a number of individual cables, which need not be insulated from each other except when functioning as high-frequency cables, in which case each of the individual wires from which the cables :are constructed is provided with a coating of lacquer, are disposed in a common cooling jacket or tube without any adverse effect on the torsionability of the entire conducting system.

Referring again to Fig. l, the conical member 24 has a substantially cylindrical extension 30 provided with an annular flange 31. The flange 31 is connected to a flange 32 which is in turn formed with an annular or cylindrical extension 33. The latter constitutes a housing for the sealing ring or like member 34. The sealing ring 34 prevents escape of the cooling medium which is located in the space formed by the member 24 and the extension 30 and permits rotation of the shaft 3 at the same time that the ends of the cables connected to the parts 21 to 24 remain stationary.

The sealing ring 35 disposed between the flanges 31 and 32 likewise prevents escape of the cooling medium to the outside. A similar function is performed by the sealing rings 36 and 37 disposed between the ilanges 27 and 28 and the intermediate member 18, respectively, and by the sealing rings 38 and 39 disposed, respectively, between the flanges 40' and 41 of the element 29 and member 13 and the insulating member 26 separating the same. The sealing ring 39 and a further sealing ring 42, the latter being disposed between the members 18 and 26, also prevent escape of any cooling medium which penetrates via the threaded portions of the members 12 and 13 into the narrow space between the members 13 and 26.

The coils 44 to 46, in `addition to holding the cables 8 against the outer surface of the tube 6, also prevent substantial expansion of the elastic tube 6 which would otherwise occur should the pressure of the cooling medium within the tube 6 exceed, to any substantial extent, the pressure exerted on the outer wall of said tube.

The advantages attendant a current lead-in unit constructed in accordance with the present invention are substantial. Flexible cables to interconnect the fixed or stationary bus bars to the conducting portions of the hollow shaft are no longer necessary, and thus the heretofore unsolved problem of providing elcacious cooling means for such cables is done away with.

Moreover, the lead-in unit according to the present invention provides large cross-sectional :and surface areas for conducting the electric current. Provision of such surface areas is especially important when high-frequency currents are to be conducted, since, due to the skin eect at high frequencies, only a surface zone of predetermined depth on each of the conducting elements performs the current-conducting function.

Furthermore, the cross-sectional diameters of the highfrequency cables located internally of the hollow shaft 3 may be made relatively large to the extent that this is permissible in view of the torsion or twisting to which the cables are to be subjected. Inasmuch as the cables are directly contacted by the cooling medium, they are thoroughly cooled. The arrangement according to the invention is especially characterized by small inductance, negligible heating during use and the facility with which it may be installed and dismantled.

The efficiency of a lead-in unit according to the present invention may be realized from the following data. The unit was constructed with the following dimensions and physical characteristics:

Outer diameter of the hollow shaft mm-- 220 Inner diameter of the hollow shaft p mm 200 Length of the hollow shaft m 0.75 Sum of the cross-sectional areas of the outer conducting cables (8) mm.2 1,500 Sum of the cross-sectional areas of the inner conducting cables (7) mm.2 945 With the above dimensions and with a current of 10,000 amps. at 10,000 c.p.s., the losses in the unit amounted to approximately 2.6 kw.

In contradistinction, the losses occurring in a current lead-in unit of known construction, employing conducting elements of the same cross-sectional areas as those given above, with dimensions of the shaft like those set forth above, and for currents of like intensity and frequency amounted to 8.6 kw. These, of course, are the losses in the unit proper. To the latter losses must be added the losses which occur in the exterior connecting cables employed to connect the stationary current collecting elements or bus bars with the movable terminals of the unit.

Such high electrical losses within the known lead-in units may be explained by the fact that, at the high frequencies involved, the losses in the electrically conductive compa-ct pipes or tubes are extremely high due to the skin effect. In the arrangement according to the invention, however, the current flows practically exclusively through the individual highly conductive cables.

A further advantage of the unit of the present invention is that capacitive losses resulting from the relative positioning of the cables 7 and S are negligibly small, if present at all, with respect to the above disclosed exemplary power loss of 2.6 kw. In any event, they comprise at most only an extremely small fraction of the aforesaid power loss which is due mainly to heating of the conducting elements.

However, should capacitive effects and losses resulting therefrom occur to any considerable extent, this would nevertheless be of advantage, since the current phase shift due to said capacitive effects would compensate for the phase shift due to the inductive effects caused by the pretorsioning or twisting of the cables 7 and 8. In other words, the power factor, cos o, would be increased, as would the efficiency of the unit.

It is, of course, apparent that it is not essential to construct the rotatable lead-in unit exactly according to the specific embodiment illustrated in Figs. l and 2 in order to attain the ultimate object of the present invention. For example, the conducting cables 8 could bc eliminated altogether, in which case the hollow shaft, which itself is made of a good electrically conductive material, would provide one of the current paths.

This would, of course, necessitate the provision of some suitable electrical connection of known construction, eg. a commutator type connection, between the bus bar 22 and the shaft 3. However, the advantages set forth above would still be present as far as the conducting cables disposed internally of the sleeve 6, through which the cooling medium flows, are concerned.

It will, furthermore, be apparent that the inlet means as well as the outlet means for the cooling medium, which may be water or any other suitable uid or liquid,

assess? may be constructed differently and positioned dierently than in the manner shown in Figs. 1 and 2. The underlying principle of the present invention requires at the very least that one part of the unit be stationary While another part thereof` may rotate with respect to said stationary part, these parts being connected by a torsionable or twistable tube or sleeve in which electric conducting elements or means are mounted and through which the cooling medium flows.

It will also be realized that the support of the cables 7 by means of the wire coil or helix 43 is not unconditionally necessary and that the plurality of cables in the interior of the tube may be replaced either by a single, torsionable conducting element of corresponding crosssection or by means of a tubular, electrically conductive Wire mesh or net. The conducting cables 8 may be similarly modified. Moreover, the cables 7 (or 8) may be uniformly or non-uniformly spaced from each other.

If desired, the helix 43 could itself be employed as a current conductor. Inasmuch as more space is available on the outer side of the tube 6, it is possible to provide a larger number of outer conducting cables which, under certain conditions, would enable the special cooling arrangement to be dispensed with.

Thus it will be seen that there has been provided, in accordance with the invention, a current lead-in unit for use with an enclosure, comprising a stationary part for location exteriorly of said enclosure and providing at least two spaced electric terminals, a rotatable hollow part having one end positioned adjacent said stationary part and another end arranged for location internally of said enclosure, and a tubular insulating element having inner and outer surfaces and extending within said rotatable hollow part from said stationary part to said other end of said rotatable part, one end of said tubular element being anchored to said stationary part and the other end of said tubular element being anchored to said rotatable part adjacent the other end thereof.

The lead-in unit further includes first torsionable conducting means arranged exteriorly of said tubular element and electrically connected to one of said terminals, second torsionable conducting means arranged interiorly of said tubular element and electrically connected to the other terminal, respective means retaining said inner and outer conducting means against said inner and outer surfaces of said tubular element, said element insulating said conducting means from each other and simultaneously insulating said terminals from each other, both said conducting means being pretorsioned through an angle equal to about one half the total angle of rotary movement of said rotatable part with respect to said stationary part and in a direction opposite to the direction of said rotary movement, and operable means connected to said rotatable part facilitating said rotary movement relative to said stationary part, whereby mechanical power consumed by said operable means when rotating said rotatable part, is reduced due to said pretorsioned conducting means.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent, is:

1. A current lead-in unit for use with an enclosure, comprising a stationary part extending for location from said enclosure therewithout and providing thereat at least two spaced electric terminals, a rotatable hollow part having one end positioned adjacent said stationary part and another end arranged for location internally of said enclosure, a tubular and elastic insulating element having inner and outer surfaces and extending within said rotatable hollow part from said stationary part to said other end of said rotatable part, first 8 torsionable conducting means arranged exteriorly of and about said tubular element and within said rotatable hollow part and electrically connected to one of said terminals, second torsionable conducting means arranged interiorly of said tubular element and electrically connected to the other terminal, said tubular element insulating said conducting means from each other, and driven means connected to said rotatable part facilitating said rotary movement relative to said stationary part.

2. A lead-in unit according to claim 1, wherein adjacent ends of said first and second conducting means are anchored in said stationary part, whereas the opposite ends of said first and second conducting means are anchored in said rotatable part and remote from said stationary part.

3. A lead-in unit according to claim 1, said driven means comprising a gear atlixed to and embracing said rotatable part.

4. A lead-in unit according to claim 1, including cooling medium conduit means for said rst and second conducting means, a first portion of said conduit means being defined by the interior of said tubular element, and a second portion of said conduit means being constituted by a space defined vbetween the outer surface of said tubular element and the inner surface of said rotatable part.

5. A lead-in unit according to claim 1, wherein both said conducting means are substantially concentrically arranged with respect to said tubular element.

6. A current lead-in unit for use with an enclosure, comprising a stationary part extending from said enclosure for location outside and adjacent said enclosure and providing at least two spaced electric terminals, a rotatable hollow part having one end positioned adjacent said stationary part and another end arranged for location internally of said enclosure, an elastic and tubular insulating element having inner and outer surfaces and extending Within and substantially coaxially with respect to said rotatable hollow part from said stationary part to said other end of said rotatable part, torsionable conducting means arranged interiorly of said rotatable part and electrically connected at one end to said terminals and at another end to said rotatable part, at least one portion of said torsionable conducting means being arranged interiorly of said tubular element, a portion of said element insulating said terminals from each other, at least said one portion of said conducting means 'being pretorsioned through an angle equal to about one half the total angle of rotary movement of said rotable part with respect to said stationary part and in a direction opposite to the direction of said rotary movement, and driven means connected to said rotatable part.

7. A lead-in unit according to claim 6, said outer surface of said tubular element being spaced from the inner surface of said rotatable hollow part, the remaining portion of said conducting means being located exteriorly of said tubular element and within the annular space defined between the outer surface of said tubular element and the inner surface of said rotatable part.

8. A lead-in unit according to claim 7, said remaining portion of said conducting means being pretorsioned in the same manner as said one portion of said conducting means.

Roberds sept. 27, 1949 Droin Mar. 20, 1956 

